Grinding machine



Sept. 27, 1966 M. KUNIHOLM GRINDING MACHINE 2 Sheets-Sheet 1 Filed Feb.13, 1964 INVENTOR martin L. Kunz'holm h 2 Sheets-Sheet 2 INVENTOR.

H oTne y Sept. 27, 1966 1.. KUNIHOLM v GRINDING MACHINE Filed Feb. 15,1964 Martin L. ffunl'holm A. E MM United States Patent 3,274,738GRINDING MACH[NE Martin L. Kuniholm, Worcester, Mass., assignor to TheHeald Machine Company, Worcester, Mass, a corporation of Delaware FiledFeb. 13, 1964, Ser. No. 344,653 6 Claims. (Cl. 51165) This inventionrelates to a grinding machine and, more particularly, to apparatusarranged to finish a surface of revolution of a workpiece by theabrasive process.

In finishing annular surfaces of revolution by grinding, there are manyadvantages to be obtained by pressing the rotating abrasive wheelagainst the surface with a constant, pre-determined force. This force isusually selected to be at a very high value but, nevertheless, alwaysbelow the force which would result in the destruction of the wheel. Thekey advantage to this method, of course, is that the finishing operationis carried out at the highest possible material-removal rate, so thatthe high capital investment in the grinding machine is occupied with oneworkpiece for as little time as possible. Furthermore, many unobvi-ousadvantages are obtained by the use of this so-called controlled forcesystem of grinding, among them being that the geometry and finish of thesurfaces are of considerably greater quality than when the workpiece isfinished by the feed rate system of grinding. Maintaining the force at aconstant, optimum value is, however, a difiicult matter, but is,nevertheless, important because the upper limit of the force that isavailable is determined by the tolerance on the force; that is to say,

the operator does not dare make the force too high for fear that, duringfluctuations of the grinding force, it may exceed the destruction forceof the wheel. These and other difficulties experienced with the priorart devices have been obviated in a novel manner by the presentinvention.

It is, therefore,.an outstanding object of the invention to provide agrinding machine using the controlled-force method of grinding in whichthe pre-determined force is maintained at a constant value within veryclose limits.

Another object of this invention is the provision of a grinding machinehaving a novel means for measuring the grinding force and using thismeasurement to regulate the grinding force.

A further object of the present invention is the provision of aninternal grinding machine using the controlled-force method, having asimple, rugged arrangement for measuring the force between the wheel andthe workpiece, and using this measurement to regulate the amount of thecontrolled force.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

The character of the invention, however, may be best understood byreference to one of its structural forms, as illustrated by theaccompanying drawings in which:

FIG. 1 is a generally schematic view of a grinding machine embodying theprinciples of the present invention,

FIG. 2 is a somewhat enlarged view of a portion of the machine, and

FIG. 3 is a vertical sectional view of a valve forming part of themachine.

Referring first to FIG. 1, wherein are best shown the general featuresof the invention, the grinding machine, indicated generally by thereference numeral 10, is shown as being of the internal type having aworkpiece support 11 carrying a workpiece 12 and mounted on a fixed base13. Also mounted on the base 13 is a wheelhead table 14 on which ismounted a wheelhead 15 having a spindle 16 on the outer end of which iscarried an abrasive wheel 17.

Extending upwardly from the upper surface of the base 13 is an abutment18 from which extends in a horizontal, transverse direction a piston rod19. The piston rod is provided at its end with a piston 21 which isslidably mounted in a cylinder 22 carried by the workpiece support 11.Extending axially through the piston rod 19 and the piston 21 is apassage 23 to which is attached a conduit 24 leading to anelectro-hydraulic servo valve 25. Also attached to the valve 25 is aconduit 26 leading from the outlet of a pump 27 whose inlet is connectedto a tank 28 of hydraulic fluid. A conduit 29 is connected to theconduit 24 and is connected through a dumping valve 31, the other sideof which is connected by a conduit 32 to the tank 28 of hydraulic fluid.The valve 3-1 is provided with an operating plunger 33 movable by thepassage of electricity through an actuating coil 34. A strong coilspring 35 resides within the cylinder 22 behind the piston 21.

The wheelhead table 14 is connected to the upper surface of the base 1-3by a spring means, indicated generally by the reference numeral 36 andshown in detail in FIG. 2. The spring means consists of a plate 37 and aplate 38 which are bolted to the upper surface of the base 13, as wellas a central plate 39 which is bolted to the undersurface of the table14. The spring means is also provided with a leaf spring 41, whichconnects the plate 37 to the plate 39 and a leaf spring 42, whichconnects the plate 38 to the plate 39. These leaf springs are located atsubstantially the same angle to the axis of the spindle 16 to permit thetable 14 and the wheelhead 15 to pivot about the center of gravity ofthe wheelhead.

The plate 38 is provided with a vertical surface 43 which extendslongitudinally of the machine and parallel to the normal axis of thespindle 16. The plate 39 is provided with a transverse surface 44 whichextends at a right angle to the surface 43, these two surfaces beinglocated on opposite sides of the centerline of the wheelhead 15. Thespring means 36 is provided with a rectangular bar 45 formed of metal,one end of which is bolted to the surface 43 of the plate 38 and oneside of which is bolted to the plate 39. The bar is provided with avertical aperture 46 located adjacent the end which is bolted to thesurface 43 of the plate 38 and another aperture 47 located adjacent theend which is bolted to the surface 44 of the plate 39. The apertures arejoined by a slot 48 defined by two parallel vertical transverse surfaces49 and 51. Mounted on the side of the bar 45, which is bolted to thesurface 44 of the plate 39, is mounted a strain gage 53 having twoelectrical leads 54 and 55. The strain gage is of the type known as anSR-4 gage and has the faculty of presenting an electrical resistancevalue from the lead 54 to the lead 55 which is in direct proportion tothe amount of strain to which it is subjected. Similarly, a strain gage56 is mounted on the surface 51 of the slot 48 and is provided withleads 57 and 58. A strain gage 59 is mounted on the surface 49 of theslot 48 and is provided with leads 61 and 62. Lastly, a side 63 of thebar 45 is provided with a strain gage 64 having leads 65 and 66. Thestrain gages 53, 56, 59 and 64 are connected to form a Wheatstonebridge, the lead 54 of the strain gage 53 being connected to the lead 65of the strain gage 64,

lead 65. Similarly, the other side of the source 67 is connected by alead 69 to the junction between the lead 57 and the lead 61. The commonpoint between the lead 66 and the lead 62 is joined by a lead 71 to aninput binding post of an amplifier 72. Similarly, the common pointbetween the lead 55 and the lead 58 is connected by a lead 73 to anotherinput binding post of the amplifier 72. This amplifiers output isconnected to either side of a coil 74 forming part of the servo valve25, as will be described hereinafter.

Y Referring to FIG. 3, it can be seen that the electrohydraulic servovalve 25 consists of a lower housing 75 and an upper block 76. Bolted inthe lower part of the housing 75 is an actuating armature 77 in the formof a steel plate, one side of which is fastened by a bolt 78 to thehousing and being free to move pivotally or hinge relative to theconnection. A heavy iron block 79 is fastened to the plate to move withit. Extending through the plate and block is an operating rod 81extending generally centrally of the valve. The coil 74 is mounted inthe housing 75 and consists of two portions 82 and 83 mounted,respectively, on cores 84 and 85 which are firmly fastened relative tothe housing 75. The portions 82 and 83 are connected electrically inseries to form the coil 74 to the ends of which are attached the outputleads of the amplifier 72. The leads are indicated in FIG. 3 as beingattached to binding posts 86 and 87 extending into the housing in adust-proof manner.

Extending through the block 76 concentric with the rod 81 is a bore 88in which is slidably carried a spool 89 mounted on the end of the rod81. Part of the bore 88 is occupied by a plug 91 having a central bore92 leading to an outlet passage 93 which is connected to the outputconduit 24. The conduit 26 is connected to an inlet passage 94 formed inthe block 76. The inlet passage 94 extends transversely and is joined toa longitudinal bore 95 which carries a restriction element 96 in theform of a threaded rod around which hydraulic fluid must pass and whichpresents a pre-determined restriction to such passage. The inner end ofthe longitudinal bore 95 is connected to a groove 97 formed in the sideof the bore 88. The spool 89 is also provided with a groove 98 and atransverse bore 99 extends through the spool and lies in the groove 98.The bore 99, in turn, communicates with a central bore 101 extendingthrough the spool and opening at the end opposite the end to which therod 81 is attached, this being the end which faces toward the plug 91.

Observation of FIG. 3 will show that the distance between the face ofthe armature block 79 and the flat ends of the cores 84 and 85associated with the coil 74 is very small (about .025 inch). Similarly,the distance between the adjacent corners of the groove 98 on the spool89 and the groove 97 in the bore 88 is a little less than that samedistance, so that as the armature moves toward the cores, the groovesbecome slightly co-extensive to permit the passage of the hydraulicfluid and to give very sensitive control. The plug 91, incidentally, isslidable in the bore, but is stopped from entering the bore too far by ashoulder 102; it is pressed into the bore by a coil spring 103 so thatthe shoulder acts as a stop.

The operation of the invention will now be readily understood, in viewof the above discussion. With the wheelhead operating, the abrasivewheel 17 also Iotates; for the purpose of the present invention, theelectric motor is contained in the wheelhead and the shaft 16 is anextension of its rotating element. The workpiece 12 is moved toward theabrasive wheel 17 by movement of the workpiece support 11 transverselyof the axis of the spindle 16 over the top surface of the base 13. Thisis brought about by introducing oil into the cylinder 22 in front of thepiston 21. Oil pressure is obtained by the use of the pump 27 pumpingoil from the body 28 into the conduit 26. The hydraulic fluid passesthrough the valve 25 and through the conduit 24 into the passage 23extending through the piston rod 19. The hydraulic fluid leaves theinner end of the passage and forces the piston 21 rearwardly; in otherwords, since the piston is fixed to the base 13 through the abutment 18,the workpiece support 11 moves forwardly, bringing the workpiece 12 intocontact with the rotating abrasive wheel 17. The workpiece itself willbe rotated in a manner well known in this art by use of a rotatingplaten or rotating rolls which engage the outer periphery. The oil, inpressing the cylinder forwardly, compresses the spring 35 between theback of the piston 21 and the other end of the cylinder. After thegrinding operation has been completed, as is indicated by a process gage(not shown) operating on the workpiece 12, electric power is passedthrough the coil 34 which operates the plunger 33 and opens the dumpingvalve 31. Since the spring 35 is always under compression and tends tocause the piston to move forward in the cylinder (or to cause thecylinder to move rearwardly relative to the piston), the oil is squeezedout through the passage 23, through the conduit 29 and the dumping valve31, and through the conduit 32 into the sump tank 28.

During the grinding operation, the oil operating in the cylinder 22brings about a pressure between the surface of the workpiece 12 which isto be finished and the surface of the abrasive wheel '17. This has theeffect of producing a torque on the spindle 16 and on the wheelhead =15.The result is that the spring means 36 is stressed and the wheelhead -15is permitted to rotate about its center of gravity, the spring elementsbeing selected so that the rotation takes place in that particularportion of the wheelhead.

From an examination of FIG. 2 it will be understood that the torque dueto the grinding force operates on the wheelhead and is passed downthrough the wheelhead table 14 to bear on the plate 39. The plate (inthe preferred embodiment) tends to rotate counter-clockwise. The torquebends the springs 42 and 4-1, among other things, and also serves tobend the bar 45. Bending of the bar 45 is accentuated by the apertures46 and 47 and the slot 48 extending between them. The result is that thestrain gages 53, 56, 59, and 64 are subjected to a. considerable strainbecause of the bending of the surfaces on which they are mounted. Allfour strain gages are mounted on a line which is in alignment with theaxis of the wheelhead. The greater the strain in the strain gages, thegreater the signal which will appear on the output ends of .theWheatstone bridge formed by them and which is introduced to theamplifier 72. This signal is increased in power by the amplifier 7 2 andthen appears on the coil 74 of the servo valve 25. When the signal isvery great, indicating that the wheel pressure against the workpiece isgreater than a pre-determined amount, the signal on the coil 74 will begreat and will draw the armature 77 closer to the cores 8'4 and 85. Thiswill cause the spool 89 .to take a position further into the .bore 88 sothat-the groove 98 and the groove 97 are co-extensive, permitting oil topass from the conduit 26 to the conduit 24 with a rather rapid flow.This will cause a rapid feeding of the workpiece support 111 forwardlyand will cause 1 an increase in '.the pressure of the wheel against theworkpiece. If, on the other hand, the force between the wheel and theworkpiece is greater than a pre-determined amount, the voltage passingout of the Wheatstone bridge and through the amplifier to energize thecoil 74 will be less, so that the spool will not permit as much fluid toflow through the valve. It is a simple matter to select the threads onthe outside surface of the restrictor element 96 in such a manner as tointroduce a restriction at all times in the flow of fluid to reducehunting, vibration, and variations in oil pressure for various reasons.

It can be seen, then, that, by use of the present invention, it ispossible to maintain and control the force between the wheel and theworkpiece and to carry on the grinding operation with a constant forceat all times. This means, of course, that the rate of feed of theworkpiece toward the wheel will vary from time to time, depending on thevarious conditions, but the important factor is that the force remainsconstant and that the force can be selected at the greatest valueconsistent with good grinding, quality of sunface, and long life of thewheel.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. An internal grinding machine, comprising (a) a base,

('b) a workpiece support adapted .to hold a workpiece, the said supportbeing mounted on the base for transverse sliding motion thereover,

(c) a wheelhead adapted to carry an abrasive wheel pivotally mounted onthe base.

(d) a hydraulic linear actuator for bringing about the sliding motionbetween the support and the base to bring about engagement between thewheel and the workpiece,

(e) a strain gage means associated with the wheelhead for indicating theforce between the wheel and the workpiece, and

(-f) a control including an electrohydraulic servo valve responsive to asignal from the strain gage means for regulating the feed means tomaintain the force between the wheel and the workpiece at apredetermined constant value.

2. An internal grinding machine as recited in claim '1, wherein pivotalmovement of the wheelhead is resisted by a spring means and the straingage means is mounted on the spring means to measure the strain therein.

3. An internal grinding machine as recited in claim 2, wherein thespring means consists of a rectangular block of metal having two spacedapertures therethrough and a narrow slot joining the apertures.

4. An internal grinding machine as recited in claim 3, wherein thestrain gage means consists of four strain gage elements, two elements ofwhich are mounted on the sides of the block in the vicinity of the slotand the other two are mounted on opposite surfaces of the slot in thevicinity of the first-named two elements.

5. An internal grinding machine as recited in claim 4 wherein the fourstrain gage elements are electrically connected to form a Wheatstonebridge, the input of the bridge being connected to a source ofelectrical power and the output being connected to deliver to the valvea signal proportional to any imbalance of the bridge.

6. An internal grinding machine as recited in claim 1, wherein the valveis provided with two spaced parallel coils electrically connected to thecontrol, an armature extending transversely across both coils andresiliently biased to a position away from the coils, an operating rodfastened at one end to the armature and passing longitudinally betweenthe coils, and a flow-regulating spool fastened to the other end of therod.

References Cited by the Examiner UNITED STATES PATENTS 2,168,596 8/ 1939Hall. 3,131,517 5/1964 Townsend et a1. 51-165 3,197,921 8/1965 Hohler etal 511-65 X 3,209,498 10/1965 Dall 51165 LESTER M. SWINGLE, PrimaryExaminer.

1. AN INTERNAL GRINDING MACHINE, COMPRISING (A) A BASE, (B) A WORKPIECESUPPORT ADAPTED TO HOLD A WORKPIECE, THE SAID SUPPORT BEING MOUNTED ONTHE BASE FOR TRANSVERSE SLIDING MOTION THEREOVER, (C) A WHEELHEADADAPTED TO CARY AN ABRASIVE WHEEL PIVOTALLY MOUNTED ON THE BASE, (D) AHYDRAULIC LINEAR ACTUATOR FOR BRINGING ABOUT THE SLIDING MOTION BETWEENTHE SUPPORT AND THE BASE TO BRING ABOUT ENGAGEMENT BETWEEN THE WHEEL ANDTHE WORKPIECE,